U.S. Pat. No. 3,011,879, published in 1961, describes gasoline compositions containing C12 to C22 linear aliphatic amines, e.g. dodecylamine, for the reduction of carburettor and other deposits, including intake (inlet) valve deposits, preferably in combination with a hydrocarbon oil and/or a metal deactivator such as a condensation product of a salicylaldehyde with an aliphatic polyamine, preferably an aliphatic diamine. The amount of amine used is between about 0.00004% and 0.02% by weight (Col. 3 lines 44 to 46) (i.e. between 0.4 ppm and 200 pm). Although it is said that the gasoline can be “with or without soluble lead compounds”, all of the gasolines of the examples (Col. 5 line 43 to Col. 9 line 57) are leaded gasolines, and the engine tests use engines with carburettors.
Modern gasolines are unleaded in order to be compatible with catalytic convertors, and fuel injection has to be used in modern spark ignition engines, in order to achieve the required stoichiometric fuel/air mixtures. A typical fuel-injected spark ignition engine has multipoint fuel injection (MPFI), in which fuel from the injectors impinges directly onto inlet valves. An unleaded base gasoline in such an engine tends to give rise to inlet valve deposits, and additives have been developed to reduce or minimise these deposits. Addition of low molecular weight aliphatic amines such as dodecylamine makes no difference to the formation of such deposits, as will be illustrated in comparative examples later in this specification.
EP-A-450 704 (Shell), published in 1991, described the use of C10 to C20 linear alkylamines, e.g. dodecylamine, as a diesel fuel additive for reducing fouling of injectors in diesel (compression ignition) engines. EP-A-450 704 specifically describes tests in an indirect injection diesel engine showing the beneficial effect in a typical blended diesel oil of the time, in accordance with BS 2869.
Although dodecylamine worked well with diesel oils of that time, those had relatively high sulphur content. With reduction of sulphur content from typical levels of about 2000 ppmw to 500 ppm or less, not only did the properties of the fuel change so that lubricity enhancers had to be incorporated in diesel fuel, but it was found (for reasons unknown) that dodecylamine failed to be effective in reducing fouling of injectors in diesel engines operating on low-sulphur fuels. Accordingly, use of dodecylamine in diesel fuel ceased, and the national patents issuing from EP-B-450 704 have been allowed to lapse.
Modern gasolines are inherently low-sulphur fuels, e.g. containing less than 150 ppmw sulphur.
A relatively new class of spark ignition engines is the class described as direct injection spark ignition (DISI) engines (also known as gasoline direct injection (GDI) engines).